There are several known types of wide field or panoramic stereoscopic cameras. A first type uses a plurality of cameras, usually a multiple of 6 cameras, disposed in a circular or spherical arrangement. Such an arrangement typically provides good quality images but is complex and expensive to set up. Also, because several cameras are used to capture the images, there may be brightness and matching errors when the panoramic stereoscopic images are constructed from the individually captured images. Such a problem is typical of any multiple camera system, whether 2D or 3D, in which images captured by different cameras are combined together to form a composite image.
It is also possible to generate panoramic stereoscopic images using a rotating head camera of well-known type. Such an arrangement is capable of providing good results but a significant amount of computer processing of the captured images is necessary in order to provide stereoscopic viewing. Also, because of the nature of such a rotating head camera, different vertical slices of the image are captured at different times and this may result in substantial visible errors if there is any significant movement in the scene or object whose image is being captured.
Another known type of stereoscopic camera arrangement makes use of wide angle lens systems such as “fisheye” lenses. However, such arrangements generally require more than one camera in order to provide a full panoramic view. Also, the resolution of the captured images is generally relatively low.
A known type of 2D system of the “catadioptric” type uses a conic section mirror, generally disposed above a camera, which may be of the “emulsion” or “opto-electric” type and which may capture still or moving images. U.S. Pat. No. 3,505,465 discloses an arrangement of this type for providing a full 360° panoramic 2D view, for example for use by tank commanders. As shown in FIG. 1 of the accompanying drawings, the reflecting surface 2 of a conic mirror 1 is axially symmetric around a vertical axis and is in the shape of a surface of rotation based on a hyperbolic section. The mirror 1 is disposed above a video camera 3 so that the axis of symmetry of the mirror 1 coincides with the optical axis of the camera 3.
The image captured by the camera 3 can be processed by means of a coordinate transformation, for example, as described hereinafter, to provide a 360° 2D panoramic image of the scene, for example around the tank. However, such an arrangement is only capable of providing 2D image capture.
Applied Optics, Vol 36, No 31, 1 Nov. 1997, pages 8275-8285, J. S. Chahl et al, “Reflective Surfaces for Panoramic Imaging” discloses another 2D arrangement in which a mirror is disposed above a camera. The mirror is circularly symmetrical about a vertical axis with a dimple on the vertical axis. This reduces the effect caused by the camera obscuring the field of view below the mirror.
EP0989436 discloses a panoramic 3D camera arrangement comprising facetted plane mirrors cooperating with a plurality of separate cameras. As shown in FIG. 2 of the accompanying drawings, the facetted mirror 1 has the shape of a pyramid, whose base is a regular polygon having any desired number of sides. The group of cameras 3 is arranged such that, for each facet, at least two of the cameras 3 capture homologous images from a direction defined by the orientation of the cooperating facet. A full panoramic 3D image may then be formed by “stitching” the individual images together. However, such an arrangement using multiple cameras 3 has the difficulties and problems of matching, synchronisation and alignment as mentioned hereinbefore. Also, the relatively large non-symmetric mirror arrangement 1 is bulky and relatively expensive.
JP11095344 discloses an arrangement similar to that disclosed in EP0989436. However, the arrangement differs in that a single camera is directed towards each facet and each facet is split and angled so that the corresponding camera captures slightly different views from the direction defined by the facet.
JP11095344 also discloses an arrangement as illustrated in FIGS. 3(a) and 3(b) of the accompanying drawings. This arrangement comprises a single camera 3 pointing upwardly along the axis of symmetry of a mirror having two separate “conic” sections 3a and 3b. The conic sections are of the same type, for example hyperbolic, but are of different sizes and shapes and are spaced apart vertically and connected together by a section 4 which has no optical function. The camera 3 thus capture a composite image in the form of two circular areas for images reflected from the sections 3a and 3b. 
The foci of the two conic mirror sections 3a and 3b are separate in space and this provides a stereo baseline from which a 3D panoramic image may be extracted. However, because the separation between the mirrors is vertical rather than horizontal, the disparity between the separate images is vertical and does not provide a horizontal baseline to permit horizontal stereoscopically related images to be extracted directly. In order to correct this and to provide stereoscopic images with horizontal disparity, additional processing including feature matching has to be performed. Such processing can be unreliable and may leave dark areas in the final images where there is no image data. Also, the captured images are of different sizes and resolutions and are therefore difficult to process together without loss of resolution or loss of quality.
WO03/054625 discloses a 3D camera arrangement as shown in FIGS. 4(a) to 4(c) of the accompanying drawings. This arrangement uses three catadioptric cameras 3a, 3b and 3c of the type shown in FIG. 6 of the accompanying drawings. The cameras are arranged at the apices of an equilateral triangle and have effective fields of view for image capture illustrated at 5a, 5b and 5c limited by the positions of the cameras. A system of this type is also disclosed by Barton et al, Proc SPIE vol. 3835, “Three-dimensional imaging, optical metrology, and inspection V”, 1999, p.84-92. However, such an arrangement requires three cameras and has the problems of the optical system matching, synchronisation and alignment as mentioned hereinbefore and, again, is difficult to set up.
Peleg et al, IEEE Transactions on Patent Analysis and Machine Intelligence, vol. 23 no. 3, March 2001, p. 279-90 ISSN: 0162-8828 discloses another technique for capturing panoramic stereoscopic images as illustrated in FIG. 5 of the accompanying drawings. This document is mainly concerned with using rotating panoramic cameras and simulations thereof. One of the disclosed techniques uses spiral shaped mirror 1a acquiring right eye circular projection P1 and spiral shaped mirror 1b acquiring left eye circular projection P2 for use with a single camera to provide capture of a wide field stereoscopic composite image. However, such a mirror arrangement is difficult to make and it is not possible to provide a full 360° panoramic view in a single shot.